The best bike to share for two people would be a folding bike. My wife and I have a Dahon for the last ten years that works well for us. It's easy and fast to adjust for size and folds up nicely in a small space to store away. Brompton is simply the best for this but I can buy three or more Dahons to one Brompton. I see Tern
folding bikes now have a folding cargo bike that look interesting.